we have a few F-150s in our fleet and have NEVER had a CV failure. These trucks spend their days in the mud and muck even acid gypsum without fail. I've run many trucks (chevy and ford) very hard (4 low full throttle, full turn with mud tires) and haven't had a failure. I get out of my trucks around 80K miles or 3 years. I'd skip anything and just let it go. I'm not sure of your location but nothing is worse then gyp on anything. CVs aren't as expensive as they used to be either.

Also, how does a expedition have 8 CVs? I count 4.